The kinetic energy budget and circulation characteristics of the tropical storm Irma during AMEX phase II

By using the data from observation on the Chinese research vessel Xiang Yang Hong No.S and other sources during AMEX phase II, the kinetic energy budget and circulation characteristics of the tropical storm Irma were analyzed. Irma formed on the ITCZ of the Southern Hemisphere. During the formative stage of the storm, the SE trades and monsoon westerlies on both sides of the ITCZ strengthened, and more importantly, there was a strong divergent flow in upper troposphere. These contributed to the intensification of Irma. At the time when Irma formed, the Richardson number(Ri) in middle and lower troposphere was much smaller than that prior to and post the formation. When Irma intensified rapidly, the area-averaged kinetic energy in the general flow increased in the whole troposphere . The largest contribution came from kinetic energy generation term, — (v · ∇⃜] .indicates that there existed a strong ageostrophic acceleration. As to the generation term , the conversion of available potential energy to kinetic energy, — ωα, made the largest contribution. This illustrates the importance of internal sources and of the ensemble effect of cumulus convection to the kinetic energy. To the increase of area-averaged eddy kinetic energy during the rapid intensification of Irma, the most important source in the whole troposphere was the dissipation term — E’⊥ that should be-interpreted as the. feeding of eddy kinetic energy from smaller to larger scale disturbances. Another important source was generation term, — -v′ · ∇⃜′], in the lower troposphere. Rather small contribution came from the energy conversion from the kinetic energy of area—mean flow to eddy kinetic energy. Therefore, the eddy kinetic energy of the developing tropical disturbance extracted both from smaller and larger scale motions. The former was much more important than the latter. In addition, the disturbance acting as a generator and exporter, generated and exported eddy kinetic energy to the environmental atmosphere.